1. Field of the Invention
The present invention relates to methods of coating a semiconductor wafer with resin for coating a surface of the semiconductor having a solder bump (a protruding electrode) or the like with resin and an improved mold therefor.
2. Description of the Background Art
Conventionally, a soft and breakable bump is protected and reinforced by coating a surface of a semiconductor chip having a bump with resin, for example in a chip size package (CSP). The operation of coating the chip with the resin is performed at the stage of manufacturing a semiconductor wafer (at a wafer level).
For example, using a mold for coating with resin shown in FIGS. 8A and 8B, the surface having a bump of the semiconductor wafer is coated with resin to produce a resin-coated wafer. Then, the resin-coated wafer is cut into a number of resin-coated chips.
More specifically, the mold shown in FIGS. 8A and 8B has an upper mold 81 and a lower mold 82, which are opposed. A film 83 for exposing a bump (for preventing a bump from being covered with resin) is applied onto the molding surface of upper mold 81. Lower mold 82 is provided with a cavity 85 for resin coating in which a semiconductor wafer 84 with a bump 88 is supplied and set, a fitting hole 86 including cavity 85, and a bottom member 87 defining a bottom of cavity 85 which vertically moves in fitting hole 86.
As shown in FIG. 8A, film 83 is applied to the molding surface of upper mold 81, and semiconductor wafer 84 is set in cavity 85 with its surface with the bump facing upward. Thereafter, a required amount of resin material 89 is supplied onto the surface with the bump, upper and lower molds 81, 82 are closed together, and resin material 89 in cavity 85 is heated to melt.
As shown in FIG. 8B, bottom member 87, along with semiconductor wafer 84 placed thereon, is moved upwardly in cavity 85, so that the leading edge of bump 88 is abutted against film 83. At the time, at least the surface of wafer 84 with the bump is coated with the resin. Thus, the portion of bump 88 that is abutting against film 83 (the leading edge of the bump) is exposed from resin (i.e., not in contact with resin) on the surface coated with resin (the surface with the bump) of resin-coated wafer 90 in cavity 85.
However, the melted resin enters a gap between fitting hole 86 and bottom member 87 (a sliding portion) and cured therein. Then, a resin burr (a hardened resin) is caused in the gap, which prevents bottom member 87 from sliding. As a result, the resin burr in the gap must frequently be removed, thereby decreasing productivity of resin-coated wafer 90.
Further, such a sliding problem prevents application of a sufficient pressure on the resin in the cavity by bottom member 87, whereby bump 88 cannot be abutted against film 83 but entirely buried in the resin. In this case, bump 88 cannot be used for external connection. As a result, the resin-coated wafer (resin-coated chip) with high quality and reliability is not provided.
One object of the present invention is to provide a method of coating a semiconductor wafer with resin for increasing productivity of a resincoated wafer, and to provide a mold used therefor.
Another object of the present invention is to provide a method of coating a semiconductor wafer with resin for ensuring a resin-coated wafer with high quality and reliability, and to provide a mold used therefor.
In the method of coating a semiconductor wafer with resin according to the present invention with which the above mentioned objects are achieved, first, a semiconductor wafer with its surface having a bump facing upward is placed in a prescribed position on the bottom surface of the cavity provided on a molding surface of one part of the mold (one mold) for resin coating. The mold has two parts whose molding surfaces are opposed. Thereafter, a required amount of resin is provided in the cavity, and a film for exposing the bump from resin is applied onto a molding surface of the other part of the mold (the other mold). In this state, the molds are closed together and the resin is heated to melt in the cavity. Then, the film is pressed against the bottom surface of the cavity by a pressing member provided on the molding surface of the other mold, so that the film is abutted against the leading edge of the bump in the cavity and the resin in the cavity is pressed through the film. Thus, the surface having the bump of the semiconductor wafer is coated with resin.
In the method of coating the semiconductor wafer with resin, preferably, the cavity is provided in the lower mold and the pressing member is provided on the upper mold. Further, the film applying step causes application of the film on the molding surface of the upper mold.
According to the above described method, the pressing member is provided on the molding surface of the upper mold, and the pressing member and the molding surface of the upper mold are not brought into contact with the resin or the melted resin because of the film for exposing the bump. Thus, the problem associated with the conventional art caused by the melted resin entering the sliding portion of the pressing member is avoided. Therefore, when the resin-coated wafer is formed with the leading edge of the bump exposed from the resin (not in contact from the resin) by abutting the film against the leading edge of the bump of the semiconductor wafer, productivity of the resin-coated wafer is increased and a resin-coated wafer with high quality and reliability is provided.
Preferably, the semiconductor wafer is coated with resin while maintaining at least the cavity in a prescribed vacuum condition. Thus, formation of voids or defective portions in the resin, which is coating the surface with the bump of the semiconductor wafer, is efficiently prevented.
In a preferred embodiment of the method of coating the semiconductor wafer with resin of the present invention, in the film applying step, the film is attracted to the molding surface of the upper mold of the mold, rumples are effectively smoothed out and avoided.
Further, in the step of supplying the semiconductor wafer, preferably, the semiconductor wafer is adsorbed to the bottom surface of the cavity, so that the semiconductor wafer is surely and stably fixed.
In another preferred embodiment of the method of coating the semiconductor wafer with resin according to the present invention, in the step of closing the upper and lower molds of the mold together, at least the cavity is brought into the prescribed vacuum condition. The vacuum is drawn with the upper and lower molds half-dosed (not completely dosed) with a prescribed space therebetween.
The mold for resin coating of the present invention which is applied to the above described method of coating the semiconductor wafer with resin includes: a stationary mold and a movable mold arranged such that molding surfaces thereof are opposed; a cavity provided in the molding surface of one mold; a heating device heating to melt the resin in the cavity; a film for exposing bump which is applied on the molding surface of the other mold; and a pressing member provided on the other mold for pressing the film against the bottom surface of the cavity.
Preferably, the mold for resin coating is further provided with a horizontally adjusting device for horizontally adjusting the surface having the bump of the semiconductor device place on the bottom surface of the cavity. Such a horizontally adjusting device allows the surface having the bump of the wafer to be horizontally adjusted even if there is a variation in thickness of the wafer. As a result, the film can efficiently be abutted against the leading edge of the bump.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.